1. Field of the Invention
The present invention relates to a terminal and a multicast address distribution server.
2. Description of the Related Art
In the past, a large majority of terminals connected to the Internet were information technology (IT) devices such as personal computers (PCs). However, in recent years, various things in the world other than IT devices have also become equipped with the communication function and have become connectable to the Internet. Such various things that are equipped with the communication function regardless of not being IT devices include wireless tags, components embedded with a sensor device or an actuator device, and IC cards. Thus, the technology by which various things other than IT devices and having the communication function communicate with each other for implementing remote monitoring, remote control, and automatic control is called the Internet of Things (IoT).
As a result of implementing the IoT, an unprecedented enormous number of terminals are connected to the Internet, and there occurs a case in which transmission of packets is done at once from a server to a plurality of terminals belonging to a particular group. As the technology for efficiently transmitting packets to a large number of terminals on a network, the multicast transmission is already known. In the multicast transmission of packets, in order to enable identification of the destination terminal group, it is necessary to set a multicast address in each terminal in the group. In the conventional technology, either a multicast address is directly set in each terminal; or a correspondence table of terminal identifiers and multicast addresses is managed on the server side, and a multicast address is assigned to each terminal according to the identifier of that terminal.
In Japanese Unexamined Patent Application Publication No. 2003-134161, a configuration is disclosed in which, with the aim of performing efficient concurrent transmission of packets to a terminal group satisfying certain conditions, an address delivery server is disposed in a network system for the purpose of performing the following operations. The address delivery serer receives, from the source terminal which is attempting to perform concurrent transmission of packets, a search condition used for searching for the destination terminal group. In response, based on the stored information related to each terminal disposed in the network, the address delivery server searches for the terminal group that matches with the search condition and generates a multicast address to be assigned to the retrieved terminal group. Lastly, the address delivery server notifies the source terminal and the destination terminal group about the generated multicast address.
In Japanese Patent No. 4886500, with the aim of eliminating the need to set a multicast address for an IP broadcast terminal, the invention is disclosed as described below. In the invention disclosed in Japanese Patent No. 4886500, IP broadcast terminals, which receive IP broadcast delivered using multicast, are disposed along with a multicast group managing device. Moreover, the multicast group managing device holds correspondence information containing the correspondence relationship between IP broadcast channel identifiers and multicast group identifiers. An IP broadcast terminal sends a query message including the IP broadcast channel identifier to the multicast group managing device. In response to the query message, the multicast group managing device decides on the multicast group identifier corresponding to the IP broadcast channel, and notifies the IP broadcast terminal about the multicast group identifier.
Besides, according to Japanese Patent No. 4886500, in a query message to be sent to the multicast group managing device, an IP broadcast terminal can include not only the IP broadcast channel but also area information related to the geographical area indicating the location of that IP broadcast terminal. In this case, the multicast group managing device can decide on the multicast group identifier by taking into account the correspondence relationship between the IP broadcast channel identifiers and the multicast group identifiers as well as by taking into account the area information. As a result, in the invention disclosed in Japanese Patent No. 4886500, a multicast group confined to a particular geographical area can be set for the IP broadcast terminal.
However, in the conventional technology including the inventions disclosed in J Japanese Unexamined Patent Application Publication No. 2003-134161 and Japanese Patent No. 4886500, it is difficult to assign a plurality of groups to each terminal. Hence, in the conventional technology, for example, the following issue arises in the case in which, for each terminal installation area, the terminal group to which the terminals belong is defined and each terminal is assigned with the terminal group to which the terminal should belong. That is, when the installation area of a particular terminal is changed, it is difficult in the conventional technology to dynamically change the terminal group to which the particular terminal belongs. Moreover, as the attribute information of terminals, it is possible to think of a variety of attribute information other than the terminal installation area. However, in the conventional technology, when the attribute information of a terminal is changed, the following issue arises. That is, in the conventional technology, dynamically resetting a new multicast address in the terminal or dynamically changing the multicast group to which the terminal belongs cannot be done in a manner adapted to the change in the attribute information.